The removal of the ad-free built-in YouTube app from iOS seems to have paid-off for Google, with the ad-enabled replacement version contributing to a tripling of the video-sharing site’s mobile ad revenue in the last six months.

YouTube owner Google reports (via Bloomberg) that more than half of all U.S. smartphone owners have used the YouTube app, and that a quarter of traffic comes from phones and tablets. Figures released earlier this year by Ooyala showed that iOS users account for two-thirds of mobile video viewing, and Google previously revealed that the same proportion of its mobile searches came from Apple’s iPhone and iPad users. iOS users are more engaged than Android users and Google clearly knows this …